In a device disclosed by Patent Document 1 (JP 5696906 B2, corresponding to US 2014/0102419 A1), fuel in a fuel tank evaporates from its liquid surface, and an upper space of the fuel tank is filled with the evaporated fuel. Thus, an inner pressure of the fuel tank increases. Since leakage of the vaporized fuel may cause atmospheric pollution, the device of the Patent Document 1 accumulates the vaporized fuel in a canister by adsorption of the vaporized fuel to the canister. When a negative pressure is produced in an intake passage of an engine, the vaporized fuel accumulated in the canister is supplied to the engine together with an intake air. Hence, the vaporized fuel is purged by combustion in a combustion chamber. Accordingly, release of the vaporized fuel to the atmosphere is limited.
In recent years, an engine loss has been reducing, and an engine negative pressure has decreased because of improvement of gasoline engine technology. Further, for example, a hybrid automobile stops an engine while running and uses another energy source to run. Therefore, generated vaporized fuel may not be purged sufficiently because of such decrease in engine negative pressure or stoppage of the engine during automobile running, and accordingly the vaporized fuel may leak to the atmosphere. Moreover, fuel efficiency of a recent gasoline engine has been increasing, and use of gasoline during a combustion process has been decreasing. Therefore, a capacity to purge the vaporized fuel has been reducing.